What bootloader are you on?
(What does it say whe you're in DL mode)
If you have Knox you cant just flash anything you like, you'll have to flash 4.3 stock rom with knox and follow instructions of how to disable knox and downgrade.
If not on knox bootloader DL a 4.1.2 rom and flash it through odin
(Your OS and Odin versions can sometimes cause the PIT not found issue)
If you haven't read prepare to be ignored, or worse.